The present invention relates to an electronically controlled throttle device, which electrically controls intake air flow into an in-vehicle engine.
Generally, the internal combustion engines for vehicles employ an electronically controlled throttle device which adjusts intake air flow by controlling a throttle valve opening by an actuator such as DC motor. The electronically controlled throttle device moves a position of the throttle valve by the actuator so as to be reach to a target opening which is calculated by an amount of accelerator pedal depression and operating status of the engine. The throttle valve opening is detected by a valve position sensor, and then a feed back control carries out.
The electronically controlled throttle device has a housing member (housing section) for the throttle valve and a housing member (housing section) for the valve drive motor, which are integrally molded, and a DC motor is put in the motor housing member. Furthermore, the throttle body is provided with a power transmission unit which transmits a driving power from the DC motor to the throttle valve, and a cover is mounted on the throttle body to protect the DC motor and the power transmission unit.
The DC motor is controlled by pulse signals from an H-bridge circuit, which is obtained by arranging switching elements in H-shape. A control amount according to a deviation between an actual opening and the target opening of the throttle valve is subjected to PID compensation calculation, converting the amount into a duty ratio, which is a ratio between ON time and OFF time, and then the ON/OFF control is carried out on the switching elements constituting the H-bridge circuit, by throttle device signals (throttle device-width modulation signals: PWM signals).
There are types of electronically controlled throttle body, i.e., in one type, an electronic control module for carrying out ON/OFF driving of the DC motor according to an opening deviation is installed on the throttle body cover, and in another type, the electronically control module is installed on an external engine control unit. The former is described, for example, in the following Patent Document 1.    [Patent Document 1] PUBLISHED JAPANESE TRANSLATION OF PCT INTERNATIONAL PUBLICATION FOR PATENT APPLICATION NO. WO 00/58614
In the meantime, when the DC motor is controlled by the pulse signals, a radiant noise may occur on startup of the switching operation and at the falling edge thereof. The radiation noise may cause a radio noise and the like. A general countermeasure against the radiant noise is based on a slew rate control, which carries out a control to make the startup slope and falling slope less steep. However, it is difficult to completely remove a noise which is generated from the DC motor itself of the electronic controlled throttle body, and a noise radiated from a wire harness (signal line) which connects the electronic controlled throttle body and the control unit. Therefore, those noises are radiated in FM radio frequency band and the like, thereby making a sound from the radio unclear.
In order to solve the problem above, an inductance is mounted between motor terminals for electrically connecting a brush of the DC motor and an external area, that is, inside the DC motor. The inductance is mounted not only to make down a slope of a large amount of current which flows in a moment, at startup and braking, but also to remove a noise. It is to be noted here that the inductance is set to be a value to the extent of not affecting a performance in response.
In the conventional art, the inductance is mounted inside the DC motor. However, a dimension of the inductance is determined based on a regulation by a coil diameter, according to a permissible current value specification and the maximum current specification at the time of using the electronic controlled throttle body. Particularly, in recent years, PWM signal frequency becomes higher, a noise level being increased, and thus a capacity of the inductance has to be enlarged. For this reason, the DC motor cannot be downsized, and further there is a problem of high-cost because environmental temperature specification of the inductance is made stricter due to self-heating of the DC motor. In addition, there is a practical problem that due to the heat of the DC motor, performance of field magnet (permanent magnet) is deteriorated, thereby reducing reliability.